Light source for recording sound on film and method of producing same



Dec. 10, 1935. s. c. WHITMAN LIGHT SOURCE FOR RECORDING SOUND ON FILM AND METHOD OF PRODUCING SAME Filed Sept. 19, 1932 O INVENTOR. Cfik/wa/vt G wfzfiXM vaw,

1 I M W ATTORNEYS.

Patented Dec. 10, i935 UNITED STATES LIGHT SOURCE FOR RECORDING SOUND N FILM AND METHOD OF PRODUCXNG SAME Stewart C. Whitman, New York, N. Y., assignor to Whitman Sound Systems, Ltd., Dover, Del., a corporation of Delaware Application September 19, 1932, Serial No. 633,911

16 Claims. (01. 179-4003) This invention relates to new and useful improvements in the art of recording sound on film and more particularly to an electronically controlled light source to accomplish these results.

An object of this invention, is to provide a photographic device capable of recording sound frequencies throughout and beyond the usual audible range.

m Another object of this invention is to provide a sound recording apparatus which can be so accurately controlled as to produce a faithful photographic sound record on film.

A further object of the invention lies in the production of a simple sound recording appa ratus which is light in weight and occupies comparatively small space.

Still another object of the invention resides in the elimination of supervision necessitated by the 2 use of complicated mechanical and optical devices in sound recording.

With these and other objects in view, my invention consists in the novel features of construction, combination and arrangement of parts 25 as will be hereinafter referred to and more particularly pointed out in the specification and claims.

In the drawing, forming a part of this application:

30 Figure 1 is a vertical longitudinal section through my device, including a schematic diagram of associated electrical circuits.

Figure 2 is a vertical transverse section taken on line 2-2 of Figure 1. 35 Figure 3 is an elevational view of the forward end of the device.

Figure 4 is a fragmentary horizontal section taken on line 4-4 of Figure 1, and

Figure 5 is a vertical transverse section taken 40 on line 5-5 of Figure l.

The above elements and their various arrangements will be more particularly described in the following disclosure.

At the present time sound recording on film is 45 accomplished by one of two methods: the mechanical light shutter which produces a variable area, record, and the variable density record which is obtained by the optical or mechanical reduction of the light from a variable source to 50 a fine slit. Both of these methods possess inherent drawbacks which limit the sound frequencies which can be successfully recorded. The variable area system is limited because of in ertia and the variable density system because of 55 the large light source area.

The present invention presents a method of actually controlling by electronic means the size of the recording light slit and also its brilliancy. Since for practical purposes there is no limit 60 to the possible reduction in slit width when electronically controlled, it is apparent that such a device would achieve a sound record having both variable area and variable density characteristics and which would include all impressed frequencies. 5

A cathode-ray oscilloscope tube of special design is utllized. Referring to the drawing in which similar reference characters designate corresponding parts throughout the several views, the numeral 6 designates the glass envelope of a 10 tube constructed according to the present invention. A glass stem 1 is sealed thereto and extends inwardly, terminating in the seal press 8 which carries sealed therein the lead-in wires 9, III, II and I2 and the support wires l3 and M. The lead-in wires I0 and H have mounted thereon an electron-emitting cathode preferably in the form of a helically wound tungsten wire as shown at IS. The lead-in wire I! and the support wire I3 have mounted thereon, and surrounding the cathode I5, a control electrode l6 which is composed of any suitable metal, such as nickel or molybdenum, and has the form of a hollow cylinder. The lead-in wire 9 and the support wire 90. extend beyond the cathode assembly with its control electrode and serve to support the anode IT. The anode I1 has the form of a disc, the diameter of which is substantially equivalent to the inner diameter of the tube envelope 6. This anode may be composed of any suitable material such as nickel. Centrally disposed on the surface of anode l1 and adjacent to the cathode i5 is provided a short cylindrical member I8 which is approximately of the same diameter as the control electrode IS. The free edge of the cylinder I8 is slightly flanged as shown at IS. The anode ll also is provided at its center with a small rectangular slot 20 of dimensions sufliciently small to be circumscribed by the cylinder lB. The actual dimensions of a slot which operates successfully are .200 inch by .010 inch.

Theelements so far described constitute the source of an electron beam of proper shape and strength for the purpose of this invention. This electron beam is obtained as follows: The cathode I5 is connected to the energizing battery through the wires 22 and 23 and is brought to the electron emitting temperature thereby. The stream of electrons is condensed to a small cylindrical beam by means of the surrounding control electrode I6 which is negatively charged by the bias battery 24 and the connecting wire 25. The anode I! is connected through the wire 26 to the positive high voltage source 21. .The strong potential gradient established between the cathode and anode accelerates the electronic stream in the direction of the anode.

The condensed electron stream arrives at the anode at high velocity striking it at the region occupied by the rectangular slot. As a consequence a thin rectangular beam of electrons is projected, still at high velocity, through the anode slot. The beam then traverses the length of the tube passing between two elongated condenser plates or control electrodes 28 and 29, which are arranged along the axis of the tube and parallel to each other. These condenser plates are provided with conductors SI and 32 which are sealed through the tube at 33 and 34. These conductors are connected across the source of the sound signals, which is shown here as an audio output transformer and is designated by the numeral 35; by the wires shown at 36 and 31. The wires 36 and 31 have connected in series therewith the condensers 38 and 39. The wire 36 also is provided with the variable source of voltage shown at 40. By these means the electron beam travelling between the condenser plates is successively flattened and widened depending on the strength of the instantaneous sound signal voltage. The forward end of the tube is provided with a metal disc 4| which may be cemented in place in any known manner. The disc 4i has mounted thereon a light transparent element which may be a diamond 42 ground in the form of a pyramid as shown in Figures 1 and 3, and preferably of electrically conducting material. The base of this pyramid extends through the disc into the tube and the base surface is substantially normal to the axis of the tube. The base is coated with a suitable luminescent or fluorescent material 43 such as powdered willemite. The stream of electrons after passing through the controlled condenser plates impinges upon this active coating causing it to glow brightly over an area corresponding to that of the wave front of the electronic beam. In appearance this glow takes the form of a brilliant thread of light the thickness of which varies with the strength of the sound signal.

This light is transmitted through the diamond and exposes the film 44 travelling past the outer edge 45 of the diamond. The diamond is used for three reasons. The optical transmission is high. The edge in contact with the fllm can be accurately ground and polished to form an extremely fine optical slit which will not wear with continued use. Finally, the diamond is electrically conductive so that, if desired, an accelerating voltage may be impressed thereon to increase the velocity of the electron stream. This voltage source is shown dotted at 46 and the connecting wire at 41. If desired, the strength of the electron beam as well as its thickness may be varied. This is accomplishedby impressing a portion of the signal voltage from 35 across the cathode l and the anode II. In the drawing this arrangement is shown in dotted lines at 48. The variable source of voltage 40 is used to focus the electronic beam on the desired portion of the active coating 43, so that the maximum amount of light falls on the optical slit at 45.

While I have illustrated above the operation of a tube designed according to my invention, I do not desire to be limited to minor details of construction and circuits but wish to cover broadly the idea of electrically controlling the shape, size and strength of an electronic beam, and thereafter translating the kinetic energy of said beam into radiant light energy for photographic sound recording purposes.

Having thus described my invention what I claim is:

1. In a system for recording sound on film, a cathode ray tube comprising a cathode at one end of said tube, an anode apertured at the point where the stream of cathode rays from said cathode will impinge upon said anode, a pair of con- 5 trol electrodes in said tube on the side of said anode opposite said cathode, the faces of said control electrodes being arranged on opposite sides of the stream of cathode rays passing through the aperture in said anode and substantially parallel with said stream, a fluorescent screen disposed atthe end of said tube opposite the end carrying the cathode, said screen being in the path of the stream of cathode rays which have passed through the aperture in said anode and between said control electrodes, and means integrally mounted in said tube for concentrating and directly transmitting without reflection substantially all of the light generated by the impinging of cathode rays on said screen to a point outside said tube and delivering it substantially as a fixed point source of light outside said tube.

2. In a'system for recording sound on film, a cathode ray tube, a cathode in one end of said tube, a fluorescent screen in the other end of said tube, an anode disposed transversely in said tube adjacent said cathode, said anode being apertured at a point nearest said cathode, a pair of control electrodes disposed in said tube between said anode and said screen, the faces of said electrodes being disposed on opposite sides of the stream of cathode rays issuing from said aperture in said anode and substantially parallel to said stream, means for applying an anode poten- 3.5 tial between said anode and said cathode, a cylindrical grid electrode surrounding said cathode, means for applying a grid biasing potential between said grid electrode and said cathode of value diiferent than said anode potential and means integrally mounted in said tube for concentrating and directly transmitting without reflection substantially all the light generated by the impinging of cathode rays on said screen to a point outside said tube and delivering it substantially as a fixed point source of light outside said tube.

3. In a system for recording sound on fllm, a cathode-ray tube, a cathode in one end of said tube, a pyramidal light transparent element set 50 into the other end of said tube with the base of said pyramidal element inside said tube and disposed transversely of said tube, the base of said pyramidal element being provided with a layer of fluorescent material, the pointed apex of said Q pyramidal element being outside of said tube, an anode disposed transversely of said tube adjacent said cathode, said anode being centrally apertured at the point thereof nearest said cathode,

a pair of control electrodes disposed in said tube between said anode and said pyramidal element, the faces of said control electrodes being on opposite sides of the stream of cathode rays emerging from the aperture in said plate and substantially parallel to said stream, said layer of fluores- 55 cent material being disposed in the path of the cathode rays which have passed between said control electrodes, whereby voltage variations impressed on said control electrodes produce corresponding variations in visible light delivered at the external apex of said pyramidal element.

4. In a system for recording sound on film, a cathode-ray tube, a cathode centrally disposed in one end of said tube, a pyramidal light transparent element set into the other end of said tube substantially at the axis thereof, the base of said pyramidal element being inside said tube substantially perpendicular to the axis thereof, the pointed apex of said pyramidal'element being outside said tube, the base or said pyramidal element being provided with a layer of fluorescent material, an anode disposed in said tube substantially normal to the axis thereof and adjacent said cathode, said anode being centrally apertured, a pair of control electrodes disposed in said tube between said anode and said pyramidal element, the faces of said control electrodes being disposed on opposite sides of the axis of said tube and substantially parallel thereto and means for applying anode potential between said anode and said cathode.

5. In a system for recording soundon fllm, a cathode-ray tube, a cathode disposed in one end of said tube, a fluorescent screen disposed in the other end of said tube, an anode disposed transversely in said tube in the proximity of said cathode, said anode being centrally apertured at the point where the normal from said cathode meets said anode, a cylindrical grid electrode surrounding said cathode and structurally and electrically insulated therefrom and having its axis substantially coinciding with the normal from said cathode to said anode, a pair of control electrodes disposed in said tube between said anode and said screen, the faces of said control electrodes being on opposite sides of the stream of cathode rays emerging from the aperture in said anode and being substantially parallel to said stream, means for applying anode potential between said anode and said cathode, means for applying grid biasing potential between said grid electrode and said cathode, and means integrally mounted in said tube for directlytransmittlng without reflection from said screen visible light directly from said fluorescent screen to a point outside said tube.

6. In a system for recording sound on fllm, a cathode-ray tube, a cathode centrally disposed in one end 01 said tube, a fluorescent screen disposed in the other end of said tube substantially normal to the axis thereof, a pair of capacity control electrodes disposed one on each side of the axis of said tube and with their facesparallel to said axis, an anode plate disposed in said tube between said cathode and said control electrodes adjacent said cathode substantially p rpendicular to the axis of said tube. said anode plate being centrally apertured substantially at the intersection of the axis of said tube with said plate, and a cylindrical control member mounted upon said anode plate on the side thereof adjacent said cathode, said control member being shorter than the diameter of said anode plate and of approximately the same diameter as the corresponding dimension of said cathode and being mounted symmetrically with reference to the axis of said tube, means for applying anode potential between said cathode and said anode, and means for conducting to a point outside said tube the visible light generated by the impingement of cathode rays emitted by said cathode upon said screen.

'7. In a system for recording sound on film, a cathode-ray tube', a cathode disposed in one end 01' said tube, a fluorescent screen integrally mounted in the other end of said tube, said screen comprising a light transparent base portion and a fluorescent portion carried by said base portion on the side nearest said cathode, said base portion being electrically conducting, a pair of capacity control electrodes disposed in said tube, one on each side of the path from said cathode to said screen and substantially parallel to said path. an anode plate disposed transversely in said tube between said cathode and said control electrodes, 5 said anode plate being apertured at the point where the path from said cathode to said screen intersects said anode plate, the base portion of said fluorescent screen being pyramidal with a point projecting outside of said tube and adapted for transmitting visible light from said screen to a point outside said tube, means for applying an anode potential between said anode plate and said cathode, and means for applying a screen accelerating potential'between said cathode and thebase portion 01' saidscreen.

v 8. In a system for recording sound on film, a cathode-ray tube, a cathode disposed in one end of said tube, a pyramidal light transparent element set into the other end of said tube with the apex of said pyramidal element outside said tube and the baseoi said pyramidal element disposed inside said tube transversely thereof, the base of said pyramidal element being provided with a layer of fluorescent material, said pyramidal element being formed of electrically conducting material, a pair of capacity control electrodes disposed in said tube one on each side of the path from said cathode to said layer of fluorescent material and with their faces substantially parallel to said path, 'an anode plate disposed in said tube transversely thereof between said cathode and said control electrodes, said anode plate being apertured at the point where the path from said cathode to said layer of fluorescent material intersects said anode plate, means for applying anode potential between said cathode and said anode, and means for applying screen accelerating potential between said cathode and said pyramidal element.

9. In a system for recording sound on fllm, a cathode-ray tube, a cathode disposed in one end of said tube, a fluorescent screen disposed in the other end of said tube, said screen comprising a light transparent base portion and a-fluorescent 5 portion carried by said base portion on the side nearest said cathode, said base portion beingelec trically conducting and extending through-and outside said tube, a pair of capacity control electrodes disposed in said tube, one on each side of the path from said cathode to said screen and substantially parallel to said path, a cylindrical grid electrode surrounding said cathode, an anode plate disposed transversely in said tube between said cathode and said control electrodes, said anode plate being apertured at the point where the path from said cathode to said screen intersects said anode plate, means for applying an anode potential between said anode plate and said cathode, means for applying. grid biasingpotential between said grid electrode and said cathode, and means for applying a screen accelerating potential between said cathode and the base portion of said screen.

10. In the recording of sound modulated electrical currents on film employing a cathode-ray tube having a cathode, a grid electrode surrounding said cathode and a fluorescent screen comprising an electrically conducting base portion inset in said tube, the method of causing photographic impressions on said fllm corresponding to said modulated currents which consists in directing a beam of cathode rays from said cathode upon said screen, modulating said beam in accordance with said currents, applying 7 a bias voltage between said grid electrode and said cathode, applying an accelerating voltage between the base portion of said screen and said cathode, and concentrating and directly transmitting the visible light formed on said screen as a modulated fixed point source of light outside of said tube.

11. In the recording of sound on film employing a cathode-ray tube having a cathode, an anode, a grid electrode surrounding said cathode. capacity control electrodes and a fluorescent screen comprising an electrically conducting base portion inset in said tube, the method of causing photographic impressions on said film corresponding to audio-frequency variations in an applied voltage wave, which consists in directing a beam of cathode rays from said cathode upon said fluorescent screen, modulating said beam of cathode rays by applying said voltage wave between said capacity control electrodes, applying a screen accelerating potential between said screen and said cathode and applying a grid bias potential between said grid electrode and said cathode for controlling the path of said beam, converting the energy of said beam of cathode rays into light or the visible spectrum by means of said fluorescent screen, and concentrating and directly transmitting the light generated by said fluorescent screen to constitute a modulated flxed point source of light outside of said tube.

12. In a system for recording sound on film, a cathode ray tube comprising a cathode at one end of said tube, an anode apertured at the point where the stream of cathode rays from said cathode would impinge upon said anode, a pair of control electrodes in said tube on the side of said anode opposite said cathode, the faces of said control electrodes being'arranged on opposite sides of the stream of cathode rays passing through the aperture in said anode and substantially parallel with said stream, a metal plate mounted in the end of said tube opposite the end carying the cathode, a light-transparent electrically conductive element mounted to pro- Ject through said plate and having a face inside said tube covered with fluorescent material and positioned in the path of said stream of cathode rays, said element terminating in a point ex.

terior of said tube, and means for applying a positive accelerating potential between said element and said cathode.

13. In a system for recording sound on fllm, a cathode-ray tube, a cathode centrally disposed in one end of said tube, a fluorescent screen disposed in the other end of said tube substantially normal to the axis thereof, a pair of capacity control electrodes disposed one on each side of the axis of said-tube and with their faces parallel to said axis, an anode plate disposed in said tube between said cathode and said control electrodes adjacent said cathode substantially perpendicular to the axis of said tube, said anode plate being centrally apertured substantially at the intersection of the axis of said tube with said plate, and a cylindrical control member mounted upon said anode plate on the side thereof adjacent said cathode, said control member being shorter than the diameter of said anode plate and of approximately the same diameter as the corresponding dimension of'said cathode and being mounted symmetrically with reference to the axis of said tube, and terminating in an outwardly flared portion pointing in the direction of said cathode, means for applying anode potential between said cathode and said anode, and means for conducting to a point outside said tube the visible light generated by the 5 impingement of cathode rays emitted by said cathode upon said screen.

14. In the recording of sound modulated electrical currents on film employing a fluorescent cathode ray tube, the method of causing photographic impressions on said film corresponding to .said modulated currents which consists in directing the beam of cathode rays from its source in said tube upon the screen of said tube, modulating said beam in accordance with said currents, controlling said beam of cathode rays by applying perpendicularly to the immediate initial p rtion thereof at its source an electrostatic field, and concentrating and directly transmitting without refiection the visible light formed on the screen of said tube as a modulated fixed point source of light outside of said tube.

15. In a system for recording sound on film,

a cathode ray tube, a helical filament cathode element mounted at one end of said tube 00- axially therewith, a fluorescent screen in the other end or said tube, an anode disposed transversely in said tube adjacent said cathode element, said anode being apertured at a point nearest said cathode element, a pair of control elecso trodes disposed in said tube between said anode and said screen, the faces of said electrodes being disposed on opposite sides of the stream of cathode rays issuing from said aperture in said anode and substantially parallel to said stream, 36 means for applying an anode potential between said anode and said cathode element, a cylindrical grid electrode element surrounding said helical filament cathode element over practically its entire length and mounted coaxially therewith, and means integrally mounted in said tube for concentrating and directly transmitting without reflection substantially all of the light generated by the impinging of cathode rays on said screen to a point outside said tube and delivering it substantially as a fixed point source of light outside said tube.

16. In a system for recording sound on film, a cathode-ray tube, a helical filament cathode disposed, in one end of said tube substantially 00- axially therewith, a fluorescent screen disposed in the other end of said tube, an anode disposed transversely in said tube in the proximity of said cathode, said anode being centrally apertured at the point where the normal from said cathode 65 meets said anode, a cylindrical grid electrode surrounding said helical cathode over practically its entire length and mounted coaxially therewith, a pair of control electrodes disposed in said tube between said anode and said screen, the faces of said control electrodes being on opposite sides of the stream of cathode rays emerging from the aperture in said anode and being substantially parallel to said stream, means for applying anode potential between said anode and said ll cathode, means for applying grid biasing potential between said grid electrode and said cathode, and means integrally mounted in said tube for transmitting without reflection from said screen visible light directly from said fluorescent screen To to a point outside said tube.

STEWART C. WHITMAN. 

